Method and apparatus for reusing green sand

ABSTRACT

A method and an apparatus for effectively reusing the green sand that would otherwise overflow the line for molding to be disposed of, even though it is fully usable, are provided. The method for reusing green sand comprising the steps of treating the green sand with ultrasonic waves in water; separating a mixture that is obtained by the step of treating the green sand with ultrasonic waves to form a suspension and to form residual particles of the sand; circulating the suspension to then proceed to the step of treating the green sand with ultrasonic waves so that the suspension is concentrated; storing the concentrated suspension; and feeding the stored suspension to green sand by a predetermined amount when green sand is mulled.

TECHNICAL FIELD

The present invention relates to a method and an apparatus toefficiently reuse green sand after molding.

BACKGROUND ART

In green sand molding, since a core is used, an organic binder that hasbeen used for forming the core dissipates so that a part of the coresand become single grains to be mixed in the green sand. Thus the totalamount of the green sand in the line for molding gradually increases, tooverflow. Thus the part of the green sand that is used in the line formolding must be disposed of. Further, the clay content is reducedbecause of the increase of the amount of the green sand. Thus clay mustbe added. This increases costs.

In this situation, materials that adhere to the surfaces of the sand arestripped, separated, and removed by mechanical means. Then the sand isreclaimed to be used for molds. The coating materials that have beenstripped and separated are collected by a dust collector in the same wayas for dust.

The coating materials that have been stripped and separated includecrushed sand as fine powder and clay that has been denatured by heatfrom poured molten metal. However, regarding active clay, which is aneffective hinder, it is difficult to separate it from the coatingmaterials that have been stripped and separated. Thus, as in PatentLiterature 1, water is added to dust that has been collected and thatincludes the coating materials that have been stripped and separated tobe reused as a paste-like sealing material for molds. But most of thedust is usually disposed of.

For example, in Patent Literature 2, a method for collecting activeclay, which is an effective hinder, from the coating materials that havebeen stripped and separated, is disclosed. In that method collected dustthat includes the coating materials that have been stripped andseparated is agitated and suspended in water. Then a supernatant liquidthat includes bentonite and organic materials is separated. Thesupernatant liquid is used in a line for molding.

However, these methods are insufficient to reuse green sand that is tobe disposed of because of overflow, by efficiently separating activeclay, which can be reused.

The present invention aims to provide a method and an apparatus foreffectively reusing green sand that would otherwise he disposed ofbecause of overflow, even though it is usable.

PRIOR-ART PUBLICATION Patent Literature

-   [Patent Literature 1]

Japanese Patent Laid-open Publication No. 2003-290872

-   [Patent Literature 2]

Published PCT Japanese Translation No. 2004-532129

SUMMARY OF INVENTION

(Italics: Claim language)

A method for reusing green sand of the present invention comprises thestep of treating the green sand with ultrasonic waves in water. It alsocomprises the step of separating to separate a mixture that is obtainedby the step of treating the green sand with ultrasonic waves to form asuspension and to form residual particles of the sand. It also comprisesthe step of circulating to circulate the suspension to then proceed tothe step of treating the green sand with ultrasonic waves so that thesuspension is concentrated. It also comprises the step of storing tostore the concentrated suspension. It also comprises the step of feedingto feed the stored suspension to green sand by a predetermined amountwhen green sand is mulled.

By treating green sand with ultrasonic waves, active clay can beefficiently separated from it to obtain a suspension that includes theactive clay. By circulating the suspension as water for treating greensand with ultrasonic waves, the suspension can be concentrated. Thus theclay of the green sand can be efficiently reused.

The method for reusing the green sand of the present inventionpreferably includes the step of removing an Oolitic layer from theresidual particles of the sand that have been separated in the step ofseparating.

By removing the Oolitic layer from the residual particles of the sand,they can be reused as core sand, etc.

An apparatus for reusing green sand of the present invention comprisesan ultrasonic washer for treating green sand with ultrasonic waves inwater, the green sand having been used. It also comprises a separatorfor separating a mixture that is obtained by the ultrasonic washer toform a suspension and to form residual particles of the sand. It alsocomprises an apparatus for circulating and making the suspensionthicker, which apparatus measures a degree of concentration of theseparated suspension, which apparatus returns the suspension to theultrasonic washer if the degree of concentration that is measuredequals, or is below, a predetermined degree of concentration, and whichapparatus feeds the suspension to a storage tank for storing thesuspension if the degree of concentration that is measured is over thepredetermined degree of concentration. It also comprises the storagetank that stores the suspension of which the degree of concentration isover the predetermined degree of concentration. It also comprises avolumetric feeder that feeds the stored suspension by a predeterminedamount when the green sand is mulled.

By treating the green sand with ultrasonic waves, active clay isefficiently removed from the green sand to cause the suspension tocontain the active clay. By using such a suspension as water for theultrasonic treatment, the suspension can be concentrated so that theclay can be efficiently used as the clay content of the green sand.

The apparatus for reusing the green sand of the present inventionpreferably comprises a system for mechanically reclaiming the green sandthat removes an Oolitic layer from the residual particles of the sandthat have been separated in the separator.

By removing the Oolitic layer from the residual particles of the sand,they can be reused as core sand, etc.

As discussed above, the present invention provides a method foreffectively reusing the green sand that would otherwise overflow fromthe line for molding to be disposed of, even though it is fully usable.

The basic Japanese patent application, No. 2017-120202, filed Jun. 20,2017, is hereby incorporated by reference in its entirety in the presentapplication.

The present invention will become more fully understood from thedetailed description given below. However, the detailed description andthe specific embodiments are only illustrations of the desiredembodiments of the present invention, and so are given only for anexplanation. Various possible changes and modifications will be apparentto those of ordinary skill in the art on the basis of the detaileddescription.

The applicant has no intention to dedicate to the public any disclosedembodiment. Among the disclosed changes and modifications, those whichmay not literally fall within the scope of the present claimsconstitute, therefore, a part of the present invention in the sense ofthe doctrine of equivalents.

The use of the articles “a,” “an,” and “the” and similar referents inthe specification and claims are to be construed to cover both thesingular and the plural form of a noun, unless otherwise indicatedherein or clearly contradicted by the context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein isintended merely to better illuminate the invention, and so does notlimit the scope of the invention, unless otherwise stated.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a system flowchart that illustrates the process for carryingout the work.

FIG. 2 is a graph that shows rates of collecting active clay from greensand by an ultrasonic treatment.

DESCRIPTION OF EMBODIMENTS

Below the present invention is discussed with reference to FIG. 1.

(1) Excess green sand that is generated in a line for molding istransported to a hopper 0 for sand that has overflowed. It istemporarily stored there.

(2) The green sand that has been stored in the hopper for the sand thathas overflowed is fed to the ultrasonic washer 1 by means of a devicefor discharging a fixed amount of the sand. Water that contains noadditives, such as a parting agent, is also fed there when the weight ofthe water is three to ten times the weight of the sand. The reason thewater that contains no additives, such as a parting agent, is so fed isbased on the cost and toxicity of the additives. If the degree ofconcentration of the suspension, which is discussed in No. (4) below, isequal to, or below, a reference value, the suspension is supplied to theultrasonic washer 1. By the ultrasonic washer 1 ultrasonic wavesgenerated at 20-400 kHz are applied to the mixture of the green sand andthe water for a period that is appropriate for the output of Ultrasonicwaves by an ultrasonic generator (the step of treating the green sandwith ultrasonic waves). The coating materials that adhere to thesurfaces of the green sand are stripped by that ultrasonic treatment.Thus the suspension wherein the coating materials that have beenstripped are suspended in the water and the residual particles of thesand from which the coating materials have been stripped are obtained.

(3) The mixture of the green sand and the water that has been subjectedto the step of treating the green sand with ultrasonic waves is fed tothe separator 2 to be separated into the suspension and the residualparticles of the sand (the step of separating). The separator 2 may be aseparator of a settling-type or of a filtering-type.

(4) The degree of concentration of the suspension is measured. If it isequal to, or below, the reference value, then the suspension iscirculated to an apparatus 5 for circulating and making the suspensionthicker and fed into the ultrasonic washer 1 so that the suspension ismade thicker (the step of circulation). The degree of concentration ofthe suspension is measured by any known densitometer, such as an opticaldensitometer that uses reflected light or transmitted light. A fixedamount of the green sand that has been stored in the hopper 0 for thesand that has overflowed is fed to the ultrasonic washer 1. The degreeof concentration of the suspension is again measured after the step oftreating the green sand with ultrasonic waves and the step ofseparating. If it is still equal to, or below, the reference value, theprocess of (4) is repeated so that the suspension is made thicker. As anexample, the reference value for the degree of concentration of thesuspension is about 20 wt %. If the degree of concentration of thesuspension is low, a problem occurs, since too much water is added whena required amount of the active clay that is contained in the suspensionis added to the green sand.

(5) A suspension that has a degree of concentration over the referencevalue is stored in the storage tank 3 (the step of storing). The storagetank 3 is preferably equipped with a stirring device to preventsettling.

(6) The suspension in the storage tank is fed to an apparatus 6 forkneading the green sand by a fixed amount by means of a volumetricfeeder 4 (the step of feeding) when the green sand is kneaded. Thevolumetric feeder 4 may be a slurry pump. The active clay that iscontained in the suspension is reused through the steps (1) to (6). Inthis way about 50% of the active clay that is to be supplied can besaved.

(7) The residual particles of the sand that have been generated in theprocess to separate the suspension from the residual particles of thesand are reclaimed by removing the Oolitic layer by means of the system7 for mechanically reclaiming the green sand (the step of removing thelayer). The Oolitic layer that strongly adheres to the surfaces of theresidual particles of the sand can be removed by the system 7 formechanically reclaiming the green sand. This system 7 preferablyperforms a drying process. It may be any known system. For example, asystem for applying force from friction to the sand may be used, whereinthe residual particles of the sand are supplied to a cup-like rotor thatrotates and wherein blades are provided above the wall of the rotor.When the rotor rotates, the residual particles of the sand scrub eachother or collide with the blades so that the Oolitic layer is crackedand stripped from the surfaces of the particles of the sand.Incidentally, the Oolitic layer is a layer of fine powder that has lowresistance to heat. This layer is strongly burned on the surfaces of theparticles of the sand. The reclaimed sand can be reused as core sand,etc.

Working Example

The degrees of separating active clay from the green sand by means ofultrasonic waves and by means of mechanical agitation are tested forcomparison. The results are shown in FIG. 2. The results were evaluatedby The Method for Evaluating Active Clay (TJFS-205), issued by TokaiBranch, Japan Foundry Engineering Society. The content of the activeclay is measured as below. 50 cm³ of a 2% solution of sodiumpyrophosphate is added to 5 g of green sand, and then is subjected toultrasonic washing for 10 minutes. The sodium pyrophosphate hasabilities to strip the coating materials on the surfaces of theparticles of the sand and to disperse them. The supernatant liquid istitrated by a methylene blue solution of 1/100 concentration. Thecontent of the active clay is determined by the consumption of thesolution.

By this method, sodium pyrophosphate, which has a function for causing adispersion, is added. However, in the present invention no dispersingagent is added. Thus distilled water, which contains no dispersingagent, is used to compare possible collections of the active clay bymeans of ultrasonic waves and by means of mechanical agitation.

The green sand is subjected to the ultrasonic treatment by usingdistilled water, which contains no dispersing agent, so that 74% of theactive clay in the green sand is included in the suspension to becollected. Thirty-eight percent of the active clay is separated andcollected by means of mechanical agitation.

From the above experiments, it is seen that 70% or more of the activeclay has been collected by the ultrasonic treatment by using distilled,water. This method is found to be very industrially useful.

The reference signs used in the present specification and the drawingsare as follows:

-   0 the hopper for the sand that has overflowed-   1 the ultrasonic washer-   2 the separator-   3 the storage tank-   4 the volumetric feeder-   5 the apparatus for circulating and making the suspension thicker-   6 the apparatus for kneading the green sand-   7 the system for mechanically reclaiming the green sand

1. A method for reusing green sand comprising the steps of: treating thegreen sand with ultrasonic waves in water; separating a mixture that isobtained by the step of treating the green sand with ultrasonic waves toform a suspension and to form residual particles of the sand;circulating the suspension to then proceed to the step of treating thegreen sand with ultrasonic waves so that the suspension is concentrated;storing the concentrated suspension; and feeding the stored suspensionto green sand by a predetermined amount when green sand is mulled. 2.The method for reusing the green sand of claim 1, further comprising: astep of removing an Oolitic layer from the residual particles of thesand that have been separated in the step of separating.
 3. An apparatusfor reusing green sand comprising: an ultrasonic washer for treatinggreen sand with ultrasonic waves in water, the green sand having beenused; a separator for separating a mixture that is obtained by theultrasonic washer to form a suspension and to form residual particles ofthe sand; an apparatus for circulating and making the suspensionthicker, which apparatus measures a degree of concentration of theseparated suspension, which apparatus returns the suspension to theultrasonic washer if the degree of concentration that is measuredequals, or is below, a predetermined degree of concentration, and whichapparatus feeds the suspension to a storage tank for storing thesuspension if the degree of concentration that is measured is over thepredetermined degree of concentration; the storage tank that stores thesuspension of which the degree of concentration is over thepredetermined degree of concentration; and a volumetric feeder thatfeeds the stored suspension by a predetermined amount when the greensand is mulled.
 4. The apparatus for reusing the green sand of claim 3,further comprising: a system for mechanically reclaiming the green sandthat removes an Oolitic layer from the residual particles of the sandthat have been separated in the separator.